When a thin walled cross section is required in a plastic part, particularly when the part is formed by injection molding, the thinning of the section usually requires a secondary operation. This may include removal of some of the plastic with a laser, a blade, or a router. The reason for the secondary operation is that when a form or slide is placed inside an injection-molding tool to form the thin walled section, the reduced area creates a spike in pressure and the flow front is disrupted. This means that the molten plastic will not fill in near the thin wall section. Also, an increase in pressure typically results in a higher localized gloss change to the surface, while the change in the flow front results in a turbulent flow causing surface deflects. In the past, these issues have been hidden with paint or other covering.
Another common surface defect in injection molded plastic parts is sink of the material. When there is a large differential change between the nominal wall stock and the thinned cross section, the part cools at different rates. This cooling difference results in a visible depression in the final part surface.
Therefore, there is a need for a method of forming a thin walled section in an injection molded plastic part that avoids these issues.